Road milling machine

Abstract

The invention relates to a road milling machine, with a milling drum housing partially surrounding a milling drum, wherein the opening between the milling drum housing and the surface of the material to be milled can be closed off by a hold-down device. The distance between the axis of rotation and the hold-down device increases in the specified direction of rotation of the milling drum at least over a section of the gap between the milling drum and the hold-down device. The particular configuration of the hold-down device leads to an improvement in transport of the milled material to the transport arrangement. The gap width increasing in the direction of rotation of the milling drum improves material flow with a relatively small power requirement and relatively low wear of the milling drum.

What is claimed is: 
     
       1. A road milling machine for milling a ground surface, comprising:
 a machine frame; 
 a milling drum housing supported from the machine frame such that an opening exists between the milling drum housing and the ground surface; 
 a milling drum positioned in the milling drum housing and rotatable in a predetermined direction of rotation about an axis of rotation; and 
 a hold-down device arranged in front of the milling drum to close the opening, the hold-down device being configured such that a gap is defined between the milling drum and the hold-down device, and a distance between the axis of rotation and the hold-down device increases in the predetermined direction of rotation at least over a section of the gap. 
 
     
     
       2. The road milling machine of  claim 1 , wherein:
 the milling drum housing is configured such that a distance between the axis of rotation and the milling drum housing increases in the predetermined direction of rotation. 
 
     
     
       3. The road milling machine of  claim 1 , further comprising:
 a guide track; and 
 wherein the hold-down device is displaceably guided on the guide track between a first position in which the hold-down device is lowered, and a second position in which the hold-down device is raised. 
 
     
     
       4. The road milling machine of  claim 3 , wherein:
 the milling drum housing has a housing lower edge; 
 the hold-down device has a hold-down device lower edge, and 
 when the hold-down device is in the raised position the hold-down device lower edge is substantially adjacent the housing lower edge. 
 
     
     
       5. The road milling machine of  claim 1 , further comprising:
 first and second guide elements located on an outer surface of the hold-down device; 
 first and second mounting elements supported from the machine frame; and 
 wherein the guide elements of the hold-down device are displaceably guided in the mounting elements. 
 
     
     
       6. The road milling machine of  claim 5 , wherein:
 the mounting elements are fastened to the machine frame. 
 
     
     
       7. The road milling machine of  claim 5 , wherein:
 the guide elements extend beyond the hold-down device so that the guide elements surround a part of the milling drum housing. 
 
     
     
       8. The road milling machine of  claim 1 , wherein:
 the hold-down device includes a lower edge and a sliding element positioned along the lower edge. 
 
     
     
       9. The road-milling machine of  claim 1 , further comprising:
 a skid positioned adjacent a lower edge of the hold-down device. 
 
     
     
       10. The road-milling machine of  claim 1 , further comprising:
 an actuator configured to raise and lower the hold-down device. 
 
     
     
       11. A road milling machine for milling a ground surface comprising:
 a machine frame; 
 a milling drum housing supported from the machine frame such that an opening exists between the milling drum housing and the ground surface; 
 a milling drum positioned in the milling drum housing and rotatable in a predetermined direction of rotation about an axis of rotation; 
 a hold-down device to close the opening the hold-down device being configured such that a gap is defined between the milling drum and the hold-down device, and a distance between the axis of rotation and the hold-down device increases in the predetermined direction of rotation at least over a section of the gap; 
 an actuator configured to raise and lower the hold-down device; and 
 a sensor configured to detect a force acting on the hold-down device when the hold-down device encounters an obstacle; and 
 a control unit configured such that the control unit generates a first control signal to raise the hold-down device when the force detected by the sensor is greater than a predetermined limit value, and a second control signal to lower the hold-down device when the force detected by the sensor is less than the predetermined limit value, so that the hold-down device rests on the ground surface with a predetermined contact force. 
 
     
     
       12. The road-milling machine of  claim 11 , wherein:
 the sensor is configured such that the force detected by the sensor is a horizontal component of the force acting on the hold-down device when the hold-down device encounters an obstacle. 
 
     
     
       13. The road-milling machine of  claim 10 , wherein:
 the actuator includes at least one piston and cylinder arrangement including a cylinder and a piston, one of the cylinder and piston having an articulated connection to the machine frame, and the other of the cylinder and piston having an articulated connection to the hold down device. 
 
     
     
       14. A road-milling machine, comprising:
 a machine frame; 
 a milling drum supported from the machine frame and rotatable about an axis of rotation so that the drum cuts upward as the milling machine moves forward; 
 a curved drum housing received about an upper part of the milling drum and defining an upper portion of a radial gap between the milling drum and the drum housing; 
 a curved hold-down plate movably extending downward from the drum housing to close a forward opening between the drum housing and a ground surface and defining a lower portion of the radial gap between the milling drum and the hold-down plate; and 
 wherein at least a part of the radial gap increases in the direction of rotation. 
 
     
     
       15. The road-milling machine of  claim 14 , wherein:
 the part of the radial gap continuously increases in the direction of rotation. 
 
     
     
       16. The road-milling machine of  claim 15 , wherein:
 the curved hold-down plate is curved as a portion of a spiral to define at least part of the continuously increasing part of the radial gap. 
 
     
     
       17. The road milling machine of  claim 16 , wherein:
 the curved drum housing is curved as a continuation of the spiral. 
 
     
     
       18. The road milling machine of  claim 15 , wherein:
 the curved drum housing is curved as a portion of a spiral to define at least part of the continuously increasing part of the radial gap. 
 
     
     
       19. The road-milling machine of  claim 14 , wherein:
 the radial gap varies between a minimum gap of no less than 15 mm and a maximum gap of no greater than 80 mm. 
 
     
     
       20. The road-milling machine of  claim 14 , wherein:
 the radial gap varies between a minimum gap of no less than about 25 mm and a maximum gap of no greater than about 50 mm. 
 
     
     
       21. The road-milling machine of  claim 14 , wherein:
 the radial gap at an upper end of the lower portion of the radial gap defined by the hold-down device is greater than the radial gap at a lower end of the upper portion of the radial gap defined by the milling drum housing.